Peter Singer's latest column on Project Syndicate is about cluster headaches.

Sufferers of cluster headaches, also known as "suicide headaches," will do anything to stop what is possibly the most painful condition known to medicine, including using illegal drugs like psilocybin and LSD. Given strong evidence that psychedelics work, why aren't doctors allowed to prescribe them?

He also urges readers to sign our open letters on clusterfree.org. Please sign and ask others to sign.